1. Field of the Invention
This invention broadly concerns an device for permitting users to self-inject a medication in a conventional syringe to a preselected depth of penetration by using a simplified triggering mechanism device permitting controlled dosing. More particularly, the present invention is concerned with an automatic injection device with a triggering mechanism which is simple for geriatric users yet includes a safety feature inhibiting premature needle projection and medication discharge.
2. Description of the Prior Art
Auto-injection devices as described herein are used by an individual to self-administer a liquid medication through a needle subcutaneously. These devices help an individual to administer the medication by pushing or driving the needle through the skin and then expressing a dosage of the medication. It can be appreciated that such devices help alleviate the fear associated with injecting oneself and provide a convenience in regard to the accuracy of the dosing.
To this end, a number of different auto-injection devices have been developed. These include the devices shown in U.S. Pat. Nos. 5,137,516 and 5,425,715. These devices provide for an injection from a medication received in an ampule or cartridge assembly. Typically, such devices are first cocked, positioned, and then triggered to administer a desired quantity of medication. The '516 patent operates by actuation of a trigger in combination with movement of two separate parts to prevent accidental actuation. However, both of these devices use a preloaded cartridge or ampule and are not readily adaptable to use with a conventional syringe. This has certain disadvantages in the types of medication which can be obtained and dispensed, as the cartridges or ampules cannot be locally filled by a pharmacist and are not adapted for receiving a commonly available syringe.
Another auto-injection device which can be used with a commercially available cartridge or syringe is shown in U.S. Pat. No. 5,358,489. This device is useful for administering medication but is difficult to handle and use, as a separate tool such as a screwdriver must be employed for recocking and a protective cap may not be retained on the tip of the needle until the desired moment of use. Thus, the '489 device is not well equipped for storage in a ready to use condition for treatment of male impotence by injection or other therapies requiring simplicity of operation and convenience of storage.
It is generally preferable to refrain from "re-capping" a syringe after an injection has been administered because there remains some risk of cross-contamination if the user's hand slips and their finger is stuck by the needle. However, replacement of the cap in self-injection devices may be desired where there are inadequate facilities for safe storage of medical sharps, or where the syringe might be set aside for some time, with the result that the user may forget that the needle is exposed.
There has thus developed a need for an auto-injection device capable of use with a standard syringe which can be filled by a local pharmacist and which can be stored with the cap in place to inhibit undesired needle "sticks".
There has also developed a need for an auto-injection device which is easy to use by geriatric patients and yet resists undesired or premature needle exposure and medication expression.
There has further developed a need for an auto-injection device which can be partially disassembled for loading and cocked, all without the need for additional tools.
There is a further need for an auto-injection device which has a trigger which is readily accessible, yet is safe to use and has a simple and inexpensive construction.
There is an additional need for an auto-injection device which includes a feature to enhance safe replacement of a needle on the syringe contained therein.